You're saying a couple of confusing things here...you're trying to grow 5 plants, and you've got a "small grow cabinet." Here's the problem.

A 400w HPS/MH switchable is great for 5-7 plants.
5 plants are not going to fit in a "small grow cabinet."
A 400w HPS/MH switchable is going to have major problems in a "small grow cabinet" unless you've got some serious venting going on

So let's start with basics. How big is your grow cabinet? If you've got 5 plants, it should be at least 26" x 36", probably more like 30" x 40". A 400w HID in a box that size will need at least a vented hood and a really good exhaust fan, and probably a cooltube. If you're factoring in those items, you haven't got a chance of keeping it at $150.

Why do you want 5 plants? Why not, say, 4 plants? Because I can tell you that 4 plants can be grown with a 250w HPS/MH, and you'll have significantly fewer heat issues...although you'll still need some serious vent issues. Grow in a 28" x 28" area with a 250, and you can get 4 3 gal pots, and veg for 30-35 days. I guess my question is whether that fifth plant is worth the heat, stress, and venting hassles.